The difference between the academic performance of poor students and wealthier students and between minority students and their non-minority peers is commonly known as the achievement gap. The current study examines the achievement gap using a large sample of students from a wide variety of school districts across the United States. It examines the achievement gap by measuring student achievement and student growth along a continuous, cross-grade measurement scale. Examination of results in mathematics and reading in grades three through eight found these differences in achievement and growth among the students studied: (1) An achievement gap exists between European-American students and African-American students in each grade and subject studied; (2) An achievement gap exists between European-American students and Hispanic students in each grade and subject studied; (3) An achievement gap exists between students in low-poverty schools and those in high-poverty schools; (4) Achievement gaps exist among European-American students, Hispanic students, and African-American students in schools with similar levels of poverty; (5) In mathematics, students enrolled in high-poverty schools tend to grow less academically during the school year than students enrolled in low-poverty schools; (6) African-American students grow less academically during the school year than students in other groups--This difference is more noticeable in mathematics than in reading; (7) Low-performing students in all groups continue to grow during summer months, but African-American students, Hispanic students, and students enrolled in high-poverty schools tend to grow less; (8) High-performing students tend to lose achievement during the summer months, with African-American students and Hispanic students losing more achievement than similar European-American students; and (9) High-performing students enrolled in high-poverty schools lose more achievement during the summer than similar students who are enrolled in low-poverty schools. Several things are clear from the findings. Central among these is that the "achievement gap" is not simply the difference in average performance between European-American students and minority students that is commonly depicted in both the popular and academic media. It affects students across the range of performance. The narrowing of the achievement gap will clearly not be an easy task and it requires concentration on all students, not just the low performers. The findings describe the nature of the gap, but do not suggest causes or potential remedies. It may be that schools can narrow the gap, but schools may not be able to close it without larger societal support. Twenty appendixes contain additional tables and figures. (Contains 24 figures and 11 tables.) [This document represents a technical report from the Northwest Evaluation Association (NWEA) Growth Research Database.]